Gripper retractor

ABSTRACT

A retractor is provided with a fluid system for opening and closing grippers in which a three-position valve is utilized with a high- and low-pressure system in such manner that fluid from an opening gripper is utilized to close another gripper. The threeposition valve is rotated between open, close and grip position by cooperating lugs carried on the valve and positioned on the retractor.

United States Patent Dale H. Pryor Houston, Tex.

Mar. 6, 1970 Oct. 5, 19-71 Youngstown Sheet and Tube Company Youngstown,Ohio Inventor Appl. No. Filed Patented Assignee GRIPPER RETRACTOR 21Claims, 8 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 2,892,535 6/1959 Cullen226/173 3,330,459 7/1967 Cullen 226/173 Primary Examiner-Richard A.Schacher Att0rneys-J. Vincent Martin, Joe E. Edwards, M. H. Gay,

Alfred 1-1. Evans and Jack R. Springgate ABSTRACT: A retract'or isprovided with a fluid system for opening and closing grippers in which athree-position valve is utilized with a highand low-pressure system insuch manner that fluid from an opening gripper is utilized to closeanother gripper. The three-position valve is rotated between open,

close and grip position by cooperating lugs carried on the valve andpositioned on the retractor.

PATENTED um 5:91:

SHEET 2 [IF 4 fla/e Pryor INVENTOR.

AffO/P/VE )J PATENTED 0m 5 I971 SHEET 3 [IF 4 GRIPPER RETRACTOR InCullen U.S. Pats. Nos. 2,892,535 and 3,330,459, retractor apparatus isshown for handling flexible pipe during drilling operation. In US. Pat.No. 2,892,535, there is disclosed a fluid system for opening and closingthe grippers in which a four-way valve is shifted to either pressurizeor exhaust the gripper systems.

Using a pressure and exhaust system results in a relatively large amountof high-pressure fluid flowing through the system to operate thegrippers. Desirably, the volume of highpressure fluid flowing throughthe system is held to a minimum.

An object of this invention is to provide a fluid system for a retractorof the type disclosed in the above-identified Cullen Patents, in whichthe amount of high-pressure fluid necessary to operate the gripper isheld to a minimum.

In accordance with this invention, a fluid system having a highandlow-pressure side which is controlled by a threeposition valve isutilized to actuate grippers to open, close and grip positions. Thefluid system substantially reduces the volume of high-pressure fluidnecessary to handle the gripper system as compared with theabove-identified Cullen Patents. This system utilizes a three-positionvalve associated with each gripper assembly which is moved between open,close and grip position during each revolution of the endless chain.

An object of this invention is to provide a simple economical system forshifting a rotary valve between three positions while the rotary valveis moving along an endless track in either direction.

Another object is to provide a valve-operating system as in thepreceding object, in which the number of valves which are in gripposition may be varied so that a lower group of grippers may remain openat the lower end of the endless chain during certain pipe-handlingoperations. Another object is to provide an operating system forretractor grippers which includes a three-position valve in which thevalve rotator is resiliently biased by an overcenter system which willassist in moving the valve rotator to an extreme position.

Another object is to provide a control system for a threeposition rotaryvalve associated with a gripper assembly of a retractor system, in whichthe valve is oscillated between grip, close and open positions with theendless chain of the retractor running in either direction.

Other objects, features and advantages of the invention will be apparentfrom the drawings, the specification and the claims.

In the drawings wherein illustrative embodiments of this invention asshown and wherein like reference numerals indicate like parts;

FIG. 1 is a side view in elevation of the retractor portion of adrilling rig;

FIG. 2 is a view taken along the lines 2-2 of FIG. 1 showing theretractor in front elevation;

FIG. 3 is a fragmentary view of one leg of the retractor and showing aportion of the trip mechanism for operating the valves;

FIG. 4 is a view illustrating operation of the three-position valveincluding the lower trip mechanism, a fragment of the endless chain andone gripper assembly, and the upper trip assembly with the valve rotatorshown in dashed lines in conjunction with each of the trip mechanisms;

FIG. 5 is a view along the lines 5-5 of FIG. 4 showing one trip assemblyin elevation and a valve rotator passing thereby in dashed lines;

FIG. 6 is a schematic flow diagram illustrating the fluid system foroperating the grippers and the assist piston for the valve rotator;

FIG. 7 is an isometric view of the rotor of one of the threepositionvalves;

FIG. 8 is a diagrammatic view of a modified form of valve rotator andtrip assemblies.

Referring first to FIG. 1, a base, indicated generally at 10, may besupported on a suitable substructure (not shown) over the site of thewell to be drilled. This base supports a mast, including legs 11 and 12.Sprockets 13, 13a, 14, and 14a are provided at the upper and lower endsof the mast. The endless chain, indicated generally at 15, is trainedover the four sprockets, in the manner taught in the Cullen Patents.

Alternate chain links 16 are carried on a pair of trunnions 17 and 18 ona gripper assembly. (FIG. 4)

Each gripper assembly may include one or more sets of opposed grippers.Preferably, two sets of opposed grippers are carried on each assembly.

Each gripper assembly is controlled by a single three-position valve,indicated generally at 23, so that the pressure acting on grippers 34 ofeach assembly is the same.

Reference is made to FIG. 6 wherein the operation of the grippers inaccordance with this invention is illustrated. It will be understoodthat the opening and closing functions take place adjacent to sprockets,while the gripping function takes place during the passage of a gripperassembly vertically between spaced sprockets on the front side of therig. While fluid is directed to only one cylinder in the schematic ofFIG. 6, such fluid will actually be directed to all of the cylinders ofeach assembly in the manner taught in the above-identified CullenPatents.

As shown in FIG. 6, each gripper 34 is connected to a pressureresponsive member or piston 35 by a suitable connecting rod 36.Preferably, this connecting rod is relatively large in diameter so thatthere is a substantial difference in the pressure responsive surface orarea on the rod side and on the other side of the piston 35. Fluid isdirected to and from the cylinder 37, in which the piston 35reciprocates through suitable conduits 38 and 39 from the three-positionvalve indicated generally at 23.

The fluid circuit for operating the grippers includes a highpressureside and a low-pressure side. The high-pressure side includes a manifoldline, indicated generally at 41, which is preferably a continuous orclosed line. Connected to the line through a suitable swivel 42 is atank 43 or source of fluid, preferably liquid, which is supplied to thehigh-pressure manifold 41 by a pump 44. Preferably, the pump willmaintain a selected pressure within the manifold line 41 at all times.

Branch lines 45 connect the high pressure manifold 41 with thethree-position valves 23 through suitable check valves 46. These checkvalves prevent back flow of fluid in the event of a failure in thesystem, a shutdown of the pump or the like, so that the system isfailsafe and the grippers will be maintained in gripping relationshipwith the pipe until the three-position valve is shifted to release thegripping action.

The fluid circuit also includes a low-pressure side, that is selectedpressure lower than the pressure in the high-pressure side. This lowpressure is maintained in a suitable closed manifold conduit 47 which isconnected through branch 48 to the three-position valves 23. The fluidfrom the low'pressure circuit is returned to tank 43 through the swivel49.

The selected lower pressure is maintained in the low pressure side ofthe circuit by the back pressure valve indicated generally at 51. Thisback pressure valve maintains the desired lower pressure and permitsexcess fluid to pass into the tank 43 through the outlet line 52.

Preferably, an accumulator 53 is provided in the circuit upstream of theback pressure valve. This accumulator will accumulate fluid from theopening of one gripper assembly and use such accumulated fluid to closeanother gripper assembly without the necessity of having one gripperassembly open at exactly the same time that another gripper assemblycloses.

The three-position valve 23 has one position in which the piston movesthe gripper towards closed position. In this position the low-pressureside of the circuit is connected to both sides of the piston 35. As theconnecting rod 36 effectively reduces the pressure responsive area ofthe piston on the rod side, the gripper is moved towards closedposition. The lowermost valve 23 is shown in this relationship with theinlet conduit 45 blocked off and the low pressure branch conduit 48connected to both lines 38 and 39.

The three-position valve means also has a second position which connectsthe low pressure side through lines 48 and 38 to the rod side of thepiston 35. The high-pressure side of the circuits, connected throughlines 45 and 39 to the other side of the piston, urges the grippertowards close position under high pressure. This is the grippingrelationship and is shown in the middle of the figure.

At the top of the figure there is shown the third position of thethree-position valve means, in which the rod side of the piston isconnected to the high-pressure side through lines 38 and 45. The otherside of the piston is connected to the lowpressure side of the circuitby connecting lines 39 and 48. This moves the gripper towards openposition.

lt will be apparent that the relative effective areas of the piston andthe differential in pressure should be correlated so that the forceexerted by the high-pressure fluid on the small area of the rod side ofthe piston is sufficient to overcome the lower pressure on the largerarea on the other side of the piston and move the piston to openposition.

There are a number of the gripping assemblies on the endless chain. Theyare constantly opening and closing. If they were timed to open and closeat exactly the same instant, the fluid from the opening assembly couldbe used to close a closing assembly. By providing the accumulator 53, itis not necessary that the opening and closing of two assemblies beexactly timed as the fluid pressure will be maintained in theaccumulator 53 to close the assemblies as the valve is shifted toclosing position.

As the fluid from an opening gripper is utilized to close anothergripper under low pressure, very little additional fluid need beintroduced into the system to close each gripper. Once closed thegripper cylinder is subjected to high pressure fluid, but as hydraulicfluid will be utilized, only a slight amount of additional fluid will beintroduced in the cylinder 37 to grip the pipe. During the opening ofthe gripper, a small amount of high-pressure fluid is utilized, but asthe connecting rod is relatively large in size the amount of fluidnecessary for this purpose is kept at a minimum. By transferringlow-pressure fluid from the opening cycle to the closing cycle, thesmall amount of additional high-pressure fluid introduced duringgripping and opening is suflicient to maintain the fluid flow to thelow-pressure side. Thus, it will be seen that the amount ofhigh-pressure fluid flow necessary to operate the grippers has beensubstantially reduced by this invention, and it is not necessary todesign the system to handle large volumes of high-pressure fluid.

The valves 23 are shown schematically. Any type valve may be used.Preferably, they are rotary valves which minimize leakage problems.

FIG. 4 shows the valve rotator for the three-position valve 23 and theassociated trip assemblies for moving the valve between its threepositions. The gripper assembly housing, indicated generally at 61,carries the two trunnions 17 and 18 which make up a portion of theendless chain. A pair of such gripper assemblies 61 is shown in FIG. 2.As in the case of the above-identified Cullen Patents, it is preferredthat the flow passageways for operating the grippers be internally ofthe housing, and the valve 23 is mounted on the housing of the gripperassembly 61, as shown in H0. 4, to establish communication between thepassageways 38 and 39 (FIG. 6) which lead to the opposite ends of thecylinder 37 for each gripper.

The valve is of the rotary type and rotates about the central axis ofshaft 62.

Nonrotatably mounted on shaft 62 is a valve rotator. This rotator has aplurality of lugs which cooperate with the trip assemblies, indicatedgenerally at 63 and 64, to move the valve actuator between open, gripand close position. The valve rotator and the lugs thereon cooperatewith the two trip assemblies to move the rotator to close position as itmoves into contact with either of the trip assemblies. The valve rotatorstays in this position for a short distance to permit fluid to flll thebackside of cylinder 37 to close the gripper. Then a lag on the rotatorcontacts a lug on the trip assembly to move the valve rotator to gripposition. The rotator remains in this position as the gripper assemblytravels between the two trip assemblies. Upon reaching the second tripassembly, a lug on the rotator engages the second trip assembly whichreturns the valve rotator to close position. This is essentially anonfunction position, but in order that the system may function with theendless chain moving in either direction it is simpler to return thevalve actuator to close position. As the valve actuator leaves thesecond trip assembly, lugs are engaged which move the actuator to theopen position. In other words, the valve actuator oscillates from opento close to grip position and then back to first close and then openposition.

In the preferred form, as shown in FIGS. 4 and 5, the valve actuator haspairs of lugs on opposite sides of the rotator. Thus, lug 65 is on theopposite side of the rotator from lug 66. Another pair of like lugs 67and 68 are positioned on opposite sides of the rotator. The lugs 65through 68 are spaced circumferentially from each other about therotator. As best shown in FlG. 5, lugs 65 and 66 rotate in a first planeof rotation of the rotator. The lugs 67 and 68 rotate in a second planeof rotation of the rotator. Preferably, the lugs 65 and 66 are carriedon rotator section 69, and the lugs 67 and 68 are carried on rotatorsection 70. By reference to FIG. 5, it will be noted that these tworotator sections are spaced along the axis of shaft 62 and rotate inseparate parallel planes.

While valves having different degrees of rotation may be utilized, theillustrated valve is rotatable through approximately and such rotationis limited by lug 67 moving between stops 71 and 72. It will be notedthat lugs 65 and 67 are spaced apart approximately the same distance aslugs 66 and 68, that is slightly less than 90. This relationship ispreferred for cooperation with the lugs of the trip assemblies.

Each trip assembly includes a pair of lugs at opposite ends forengagement with the rotator lugs. Thus, referring to FIG. 5, the endsurface 73 and the end surface 74 of the trip assembly each provide alug for engagement with a rotor lug. The face of the trip assembly 75,which confronts the valve rotator, is planar for a purpose which will beexplained hereinafter. Lugs 76 and 77 extend outwardly from this planarsurface 75 toward the valve rotator. it will be noted that the lugs 76and 77 are positioned on opposite sides of the upper trip assembly 64with the lug 76 lying in the path of travel of rotator section 70, andthe lug 77 lying in the path of travel of the rotator section 69. Thetwo trip assemblies are identical: therefore, the parts thereof havebeen given the same numbers. The two trip assemblies only differ intheir positioning, that is they face inopposite directions. Thus, thelower trip assembly lug 76 lies in the path of rotator section 69. Thelower trip assembly 63 cooperates with lugs 65 and 67 to shift the valverotator and the upper trip assembly 64 cooperates with lugs 66 and 68 torotate the valve rotator.

Due to the 90rot'ation of the valve 23 in movement between its threepositions, it is desirable to utilize the above described assembly tomove the valve rotator to its intermediate position but in moving to thetwo extreme positions it is preferred that the lugs be assisted byadditional means.

To assist the rotator in movement to its full extreme positions, an overcenter resilient means is provided, which when moved to either side ofcenter, exerts a resilient force on the valve rotator to assist the lugsin moving the valve rotator to its two extreme positions. This resilientmeans may take any desired form, such as the fluid cylinder indicatedgenerally at 78. This fluid cylinder is provided with a pivotable anchorpoint 79 (the details of which are not shown) which permits the cylinder78 to pivot relative to the gripper assembly. The piston rod 81 isconnected to lug 67 by pin 82. By reference to the upper portion of FIG.4, it will be noted that the connection points 79 and 82 and the centerof rotation 62 of the rotator are in line when the rotator is in itsintermediate or center position. As these points are in line,substantially no force is exerted tending to rotate the rotor in eitherdirection. The rotor will normally be fairly difficult to turn due topacking therein. Such packing will prevent rotation of the rotor fromthis intermediate position until it is acted upon by one of the tripassembly lugs. If desired, a suitable detent may also be provided in thevalve to hold it in this intermediate position.

In the illustrated form of the invention, the three-position valve rotoris prevented from moving from its intermediate position by the planarsurface 75 of the trip assembly which lies very close to the rotatorlugs which cooperate therewith as the rotator passes by the tripassembly. If there is any tendency for the rotator to move from itsintermediate position, the pair of lugs adjacent the trip assembly willengage the surface 75, and the rotator will be prevented from leavingits intermediate position until after the lead rotator lug has passedover the trip assembly.

Referring to FIG. 6 again, it will be noted that the cylinder 78receives pressure from the low-pressure side of the fluid system. Thus,the accumulator 53 will be constantly urging fluid into the severalcylinders 78 and urging the rotator toward either of its extremepositions once the rotator is moved out of the intermediate position.

During certain pipe handling operations, it is desirable that several ofthe grippers in the lowermost position remain open for a short distanceabove the lower sprockets to facilitate the handling of the drill pipe.For this purpose, the lower trip assembly 63 is mounted on a member 80with a suitable slide arrangement indicated generally at 60. As bestshown in FIG. 4, the lower trip assembly 63 is supported on a plate 101which is slidable on the vertical member 80. As shown in FIG. 3, thelower trip assembly is moved vertically by an articulating arm having aninboard portion 102 and outboard portion 83, which is pinned to plate101. A suitable actuator cylinder is indicated generally at 84. Thecylinder is attached to the inboard ann 102 at 85 and extension of thepiston rod 86 in the cylinder raises the articulated arm which ispivoted to the frame as indicated generally at 87.

- ln operation of this form of the invention, an open gripper assemblymay be considered to be moving upwardly in FIG. 4. As it approaches thelower trip assembly 63, the lug 67 is in engagement with stop 72. Thelug 65 will be in approximately a 12 o'clock position, as viewed in FIG.4, and thus as the assembly moves upward the lug 65 clears the lowertrip assembly. However, the lug 67 of the rotator comes in contact withsurface 73 of the trip assembly, and continued upward movement of thegripper forces rotation of the rotator to the positions shown in dottedlines adjacent to the lower trip assembly. In this position, thegrippers are closing. The valve rotator remains in its intermediateposition until this same lug 67 strikes the lug 77 at the upper end ofthe lower trip assembly starting the valve rotator in its counterclockwise rotation. The rotator is partially rotated by engagement ofthe lugs, and after a short amount of rotation has taken place the lugis assisted by the resilient force exerted by cylinder 78 to move therotator to the solid line position of FIG. 4 at which time the grippingassembly is in its grip position.

As the rotator reaches the upper trip assembly, the lug 66 strikessurface 73 on the upper trip assembly and the rotator is moved to theupper dotted line position of FIG. 4. At this time, the valve has beenreturned to close position. As the rotator leaves the upper tripassembly, the lug 66 strikes lug 77 of the upper trip assembly andbegins the rotation of the rotor toward open position. After thisrotation is begun, the cylinder 78 and its associated piston urge therotator toward a full open position until the lug 67 strikes the stop72.

During reverse travel of the endless chain from that just explained, theother two lugs are cooperative with the trip assemblies to shift thevalve rotator. Thus, when the valve rotator is moving downwardly, asviewed in FIG. 4, the lug 68 of the rotator cooperates with surface 74of the upper trip assembly to move the rotator from open to closeposition and then to grip position as the lug 68 of the rotator passesover lug 76 on the trip assembly. Then when the rotator reaches thelower trip assembly, the lug 65 engages surface 74 to move the rotatorto close position, and then the lug 65 engages lug 76 to move therotator to open position.

It will be appreciated that the system illustrated in FIG. 4 is one inwhich close tolerances are not required and flexure of the endless chainwill not effect the operation. For this reason, the system shown in FIG.4 is preferred. However, other systems of lugs could be utilized, suchas the rack-and-pinion system shown in FIG. 8. In this instance, thevalve rotator is in the form of a pinion 88, and the two trip assembliesare in the form of racks, indicated generally at 89 and 9l. Each rackhas a plurality of teeth 92 and 93 at its extremities and anintermediate section 94 which has no teeth and does not engage thepinion 88.

The rack teeth 93 provide lugs on the lower assembly which rotate thepinion 88 and move the valve operator from open to close position. Thepinion remains in the close position as it passes by the toothlesssection 94 of the rack. At the upper section of the rack, the teeth 92further rotate the pinion to the grip position. As the pinion reachesthe upper trip assembly, the lower teeth 93 return the pinion to closeposition and the upper teeth 92 rotate the pinion to the open position.Of course, a number of rack teeth could be utilized to fully rotate thepinion, or, as an alternative, the pinion could be started in itsrotation by rack teeth and then moved to the full extreme position by aresilient assist such as is provided in the FIG. 4 form of thisinvention.

From the above, it will be appreciated that the planar surface 75 isoptional but is preferred as it will positively prevent the valve rotorfrom moving out of its intermediate position before the fluid system hashad an opportunity to move the grippers to close position. It will beobvious that the several lugs provided on each trip assembly could beprovided in any desired manner and take any desired form.

The resilient means 78 is optional, but it is preferred where the valvehas a substantial arc of movement such as the approximate illustrated.Where such resilient assist is not used the resistance of the valve torotation may be depended upon to hold it in its three positions,'orsuitable internal detents may be provided in the valve if desired.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What is claimed is:

1. A retractor comprising:

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

a fluid system for controlling the grippers including threepositionrotary valves on the endless chain;

said system in said three valve positions exerting close, grip,

and open forces on said grippers;

and means for shifting each valve between said three positionscomprising;

a valve rotator,

a plurality of lugs on said rotator,

a first trip assembly on the support having at least one lug forengaging a rotator lug and moving the rotator to closed position and atleast another lug spaced from said one lug for engaging a rotator lugand moving the rotator to grip position as the rotator moves past thefirst trip assembly,

and a second trip assembly on the support having at least one lug forengaging a rotator lug and moving the rotator to said closed positionand at least another lug spaced from said one lug of the second tripassembly for engaging a rotator lug and moving the rotator to openposition as the rotator moves past the second trip assembly,

said trip assemblies moving said rotator to said close, grip and openpositions with the endless chain moving in either direction.

2. The retractor of claim 1 wherein means are provided for holding saidvalve rotator in said open, close and grip positions until the rotatoris engaged and rotated by said trip assembly lugs.

3. The retractor of claim 1 wherein one of said trip assemblies ismovable toward and away from the other trip assembly to control thenumber of rotators which are simultaneously in gripping position.

4. The retractor of claim 1 wherein means are provided for holding saidvalve rotator in said closed position until the rotator contacts a lugon one of said trip assemblies;

and means for provided for assisting said lugs and moving said rotatorto full open and full grip position after initial rotation of saidrotator from said closed position and for holding said rotator in fullopen and full grip position until the rotator contacts a lug on one ofsaid trip assemblies.

5. The retractor of claim 1 wherein means are provided for holding saidvalve rotator in said closed position until the rotator contacts a lugon one of said trip assemblies;

and resilient means are associated with each three-position valve andconnected to each rotator with the anchor point for the resilient means,the connection point of the resilient means to the rotator and thecenter of rotation of the rotator being substantially in line when therotator is in closed position and effective to urge the rotator towardgrip or open position after the rotator has moved to a position in whichsaid connection and anchor points and center of rotation are no longerin line.

6. The retractor of claim 1 wherein resilient means are associated witheach three-position valve and connected to each rotator with the anchorpoint for the resilient means, the connection point of the resilientmeans to the rotator and the center of rotation of the rotator beingsubstantially in line when the rotator is in closed position andeffective to urge the rotator toward grip or open position after therotator has moved to a position in which said connection and anchorpoints and center of rotation are no longer in line.

7. The retractor of claim 1 wherein a fluid system having ahigh-pressure side and a low-pressure side is connected to saidthree-position valves and lower pressure fluid from grippers movingtoward open position is utilized to move other grippers toward closedposition.

8. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

a fluid system for controlling the grippers including threepositionrotary valves on the endless chain;

said system in said three valve positions exerting close, grip and openforces on said gripper;

and means for shifting each valve between such three positionscomprising;

a pinion type valve rotator,

a pair of spaced racks cooperative with said rotator,

each rack having teeth at its end for engagement with said rotator and aspace between said teeth in which the rotator does not engage the rack,

said racks having their teeth facing in opposite directions andsuccessively engaging said rotator to move at first to closed position,then to grip position, then to close position, and then to open positionwith the endless chain moving in either direction.

9. The retractor of claim 8 wherein one of said racks is movable towardand away from the other rack to control the number of rotators which aresimultaneously in gripping position.

10. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

a fluid system for controlling the grippers including threepositionrotary valves on the endless chain;

said system in said three valve positions exerting close, grip and openforces on said grippers;

and means for shifting each valve between said three positionscomprising;

a valve rotator,

a pair of lugs on opposite sides of said rotator lying in a first planeof rotation of said rotator,

a second pair of lugs on opposite sides of said rotator lying in asecond plane of rotation of said rotator,

said lugs being spaced from each other circumferentially of the rotator,

a pair of spaced trip assemblies each having a planarsurfacesubstantially perpendicular to said planes of rotation and adjacent oneof each pair of lugs when the rotator is in closed position and movingpast said surface,

the ends of said planar surface acting as lugs to engage said rotatorlugs and move the rotator to closed position,

and a lug at each end of each trip assembly extending toward the rotatorfrom said planar surface with one of the extending lugs lying in saidone plane of rotation and the other of the extending lugs lying in saidsecond plane of rotation,

said extending lugs engaging the trailing rotator lug as it reaches theend of said planar surface to move the rotator to either grip or openposition.

11. The retractor of claim 10 wherein the fluid system has ahigh-pressure side and a low-pressure side connected to saidthree-position valves and low-pressure fluid from grippers moving towardopen position is utilized to move other grippers toward closed position.

12. The retractor of claim 10 wherein means are provided for holdingsaid valve rotator in said open, close, and grip positions until therotator is engaged and rotated by said trip assembly lugs.

13. The retractor of claim 10 wherein one of said trip assemblies ismovable toward and away from the other trip assembly to control thenumber of rotators which are simultaneously in grip position.

14. The retractor of claim 10 wherein resilient means are associatedwith each three-position valve and connected to each rotator with theanchor point for the resilient means, the connection point of theresilient means to the rotator and the center of rotation of the rotatorbeing substantially in line when the rotator is in closed position andeffective to urge the rotator toward grip or open position after therotator has moved to a position in which said connection and anchorpoints and center of rotation are no longer in line.

15. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

a fluid system for controlling the grippers including threepositionrotary valves on the endless chain;

said system in said three valve positions exerting close, grip and openforces on said grippers;

and means for shifting each valve between said three posi'tionsicomprising;

a valve rotator,

a plurality of lugs on said rotator,

a first trip assembly having a first lug for engaging a rotator lug tomove the rotator to close position and a second lug engaging a rotatorlug to move the rotator to grip position,

and a second trip assembly having lug means for engaging a rotator lugto move the rotator to open position.

16. The retractor of claim 15 wherein the fluid has a highpressure sideand a low-pressure side connected to said threeposition valves andlow-pressure fluid from grippers moving toward open position is utilizedto move other grippers toward closed position.

17. The retractor of claim 15 wherein means are provided for holdingsaid valve rotator in said open, close and grip position until therotator is engaged and rotated'by said trip assembly lugs.

18. The retractor of claim 15 wherein one of said trip assemblies ismovable toward and away from the other trip as sembly to control thenumber of rotators which are simultaneously in grip position.

19. The retractor of claim wherein a means are provided for holding saidvalve rotator in said closed position until the rotator contacts a lugon one of said trip assemblies and means are provided for assisting saidlugs in moving said rotator to full open and full grip position afterinitial rotation of said rotator from said closed position and forholding said rotator in full open and full grip position until therotator contacts a lug on one of said trip assemblies.

20. The retractor of claim 15 wherein a means are provided for holdingsaid valve rotator in said closed position until the rotator contacts alug on one of said trip assemblies;

and resilient means associated with each three-position valve andconnected to each rotator with the anchor point for the resilient means,the connection point of the resilient means to the rotator and thecenter of rotation of the rotator being substantially in line when therotator is in closed position and effective to urge the rotator towardgrip or open position after the rotator has moved to a position in whichsaid connection and anchor points and center of rotation are no longerin line.

21. The retractor of claim 15 wherein resilient means are associatedwith each three-position valve and connected to each rotator with theanchor point for the resilient means, the connection point of theresilient means to the rotator and the center of rotation of the rotatorbeing substantially in line when the rotator is in closed position andeffective to urge the rotator to grip or open position after the rotatorhas moved to a position in which said connection and anchor points andcenter of rotation are no longer in line.

1. A retractor comprising: a support; an endless chain on the support; aplurality of grippers carried by the chain; a fluid system forcontrolling the grippers including threeposition rotary valves on theendless chain; said system in said three valve positions exerting close,grip, and open forces on said grippers; and means for shifting eachvalve between said three positions comprising; a valve rotator, aplurality of lugs on said rotator, a first trip assembly on the supporthaving at least one lug for engaging a rotator lug and moving therotator to closed position and at least another lug spaced from said onelug for engaging a rotator lug and moving the rotator to grip positionas the rotator moves past the first trip assembly, and a second tripassembly on the support having at least one lug for engaging a rotatorlug and moving the rotator to said closed position and at least anotherlug spaced from said one lug of the second trip assembly for engaging arotator lug and moving the rotator to open position as the rotator movespast the second trip assembly, said trip assemblies moving said rotatorto said close, grip and open positions with the endless chain moving ineither direction.
 2. The retractor of claim 1 wherein means are providedfor holding said valve rotator in said open, close and grip positionsuntil the rotator is engaged and rotated by said trip assembly lugs. 3.The retractor of claim 1 wherein one of said trip assemblies is movabletoward and away from the other trip assembly to control the number ofrotators which are simultaneously in gripping position.
 4. The retractorof claim 1 wherein means are provided for holding said valve rotator insaid closed position until the rotator contacts a lug on one of saidtrip assemblies; and means for provided for assisting said lugs andmoving said rotator to full open and full grip position after initialrotation of said rotator from said closed position and for holding saidrotator in full open and full grip position until the rotator contacts alug on one of said trip assemblies.
 5. The retractor of claim 1 whereinmeans are provided for holding said valve rotator in said closedposition until the rotator contacts a lug on one of said tripassemblies; and resilient means are associated with each three-positionvalve and connected to each rotator with the anchor point for theresilient means, the connection point of the resilient means to therotator and the center of rotation of the rotator being substantially inline when the rotator is in closed position and effective to urge therotator toward grip or open position after the rotator has moved to aposition in which said connection and anchor points and center ofrotation are no longer in line.
 6. The retractor of claim 1 whereinresilient means are associated with each three-position valve andconnected to each rotator with the anchor point for the resilient means,the connection point of the resilient means to the rotator and thecenter of rotation of the rotator being substantially in line when therotator is in closed position and effective to urge the rotator towardgrip or open position after the rotator has moved to a position in whichsaid connection and anchor points and center of rotation are no longerin line.
 7. The retractor of claim 1 wherein a fluid system having ahigh-pressure side and a low-pressure side is connected to saidthree-position valves and lower pressure fluid from grippers movingtoward open position is utilized to move other grippers toward closedposition.
 8. A retractor comprising; a support; an endless chain on thesupport; a plurality of grippers carried by the chain; a fluid systemfor controlling the grippers including three-position rotary valves onthe endless chain; said system in said three valve positions exertingclose, grip and open forces on said gripper; and means for shifting eachvalve between such three positions comprising; a pinion type valverotator, a pair of spaced racks cooperative with said rotator, each rackhaving teeth at its end for engagement with said rotator and a spacebetween said teeth in which the rotator does not engage the rack, saidracks having their teeth facing in opposite directions and successivelyengaging said rotator to move at first to closed position, then to gripposition, then to close position, and then to open position with theendless chain moving in either direction.
 9. The retractor of claim 8wherein one of said racks is movable toward and away from the other rackto control the number of rotators which are simultaneously in grippingposition.
 10. A retractor comprising; a support; an endless chain on thesupport; a plurality of grippers carried by the chain; a fluid systemfor controlling the grippers including three-position rotary valves onthe endless chain; said system in said three valve positions exertingclose, grip and open forces on said grippers; and means for shiftingeach valve between said three positions comprising; a valve rotator, apair of lugs on opposite sides of said rotator lying in a first plane ofrotation of said rotator, a second pair of lugs on opposite sides ofsaid rotator lying in a second plane of rotation of said rotator, saidlugs being spaced from each other circumferentially of the rotator, apair of spaced trip assemblies each having a planar surfacesubstantially perpendicular to said planes of rotation and adjacent oneof each pair of lugs when the rotator is in closed position and movingpast said surface, the ends of said planar surface acting as lugs toengage said rotator lugs and move the rotator to closed position, and alug at each end of each trip assembly extending toward the rotator fromsaid planar surface with one of the extending lugs lying in said oneplane of rotation and the other of the extending lugs lying in saidsecond plane of rotation, said extending lugs engaging the trailingrotator lug as it reaches the end of said planar surface to move therotator to either grip or open position.
 11. The retractor of claim 10wherein the fluid system has a high-pressure side and a low-pressureside connected to said three-position valves and low-pressure fluid fromgrippers moving toward open position is utilized to move other gripperstoward closed position.
 12. The retractor of claim 10 wherein means areprovided for holding said valve rotator in said open, close, and grippositions until the rotator is engaged and rotated by said trip assemblylugs.
 13. The retractor of claim 10 wherein one of said trip assembliesis movable toward and away from the other trip assembly to control thenumber of rotators which are simultaneously in grip position.
 14. Theretractor of claim 10 wherein resilient means are associated with eachthree-position valve and connected to each rotator with the anchor pointfor the resilient means, the connection point of the resilient means tothe rotator and the center of rotation of the rotator beingsubstantially in line when the rotator is in closed position andeffective to urge the rotator toward grip or open position after therotator has moved to a position in which said connection and anchorpoints and center of rotation are no longer in line.
 15. A retractorcomprising; a support; an endless chain on the support; a plurality ofgrippers carried by the chain; a fluid system for controlling thegrippers including three-position rotary valves on the endless chain;said system in said three valve positions exerting close, grip and openforces on said grippers; and means for shifting each valve between saidthree positions comprising; a valve rotator, a plurality of lugs on saidrotator, a first trip assembly having a first lug for engaging a rotatorlug to move the rotator to close position and a second lug engaging arotator lug to move the rotator to grip position, and a second tripassembly having lug means for engaging a rotator lug to move the rotatorto open position.
 16. The retractor of claim 15 wherein the fluid has ahigh-pressure side and a low-pressure side connected to saidthree-position valves and low-pressure fluid from grippers moving towardopen position is utilized to move other grippers toward closed position.17. The retractor of claim 15 wherein means are provided for holdingsaid valve rotator in said open, close and grip position until therotator is engaged and rotated by said trip assembly lugs.
 18. Theretractor of claim 15 wherein one of said trip assemblies is movabletoward and away from the other trip assembly to control the number ofrotators which are simultaneously in grip position.
 19. The retractor ofclaim 15 wherein a means are provided for holding said valve rotator insaid closed position until the rotator contacts a lug on one of saidtrip assemblies and means are provided for assisting said lugs in movingsaid rotator to full open and full grip position after initial rotationof said rotator from said closed position and for holding said rotatorin full open and full grip position until the rotator contacts a lug onone of said trip assemblies.
 20. The retractor of claim 15 wherein ameans are provided for holding said valve rotator in said closedposition until the rotator contacts a lug on one of said tripassemblies; and resilient means associated with each three-positionvalve and connected to each rotator with the anchor point for theresilient means, the connection point of the resilient means to therotator and the center of rotation of the rotator being substantially inline when the rotator is in closed position and effective to urge therotator toward grip or open position after the rotator has moved to aposition in which said connection and anchor points and center ofrotation are no longer in line.
 21. The retractor of claim 15 whereinresilient means are associated with each three-position valve andconnected to each rotator with the anchor point for the resilient means,the connection point of the resilient means to the rotator and thecenter of rotation of the rotator being substantially in line when therotator is in closed position and effective to urge the rotator to gripor open position after the rotator has moved to a position in which saidconnection and anchor points and center of rotation are no longer inline.